248 TRANSACTIONS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
beyond the shadow of a doubt. Towards the western boundaries of 
our own shire the first exposure of this rock which we meet with is 
that seen on the north-east side of Ben Lui. Further to the north¬ 
west of Tyndrum we find these same schists faulted down against a 
series of quartzites and trending in a north north-east direction. 
Passing from Tyndrum down the valley of Glen Dochart we find the 
lower grounds of the valley occupied by the quartz schists and more 
arenaceous types of schist; on the higher grounds, however, of the 
ridge which separates Glen Dochart from Glen Lochay the band of 
fine sericite schist again appears. From this point it strikes north-east¬ 
wards, crossing the valley of the Lochay a little above the falls, where 
they are exposed in some fine sections. The steady north-east strike 
of these rocks carries them along the ridge on the north side of Loch 
Tay, where they are well seen in the many escarpments and beds of 
streams descending from Craig-na-Caillach, Meall-nan-Tarmachan, 
Beinn Ghlass, and Ben Lawers. The outcrop of this bed of schist 
traced still further towards the north-east, trends along the ridge which 
separates the valleys of the Tummel and the Tay, crossing these two 
valleys near their junction above Pitlochry, and from this point 
stretching through Ben Vrackie onwards to Canlochan and the Clova 
mountains. It has been termed by the Geological Survey the B.en 
Lawers and Canlochan Schist from its well-defined outcrop at these 
points. 
It is now a considerable number of years since I first recognized 
the existence of this well-marked band of sericite schist on the sum¬ 
mits of the Breadalbane mountains, where it lies immediately above 
the quartz schists and more arenaceous mica schists, with garnets 
and beds of the Loch Tay limestone, which form the lower grounds, 
and in the ridge to the north of Loch Tay it is not until we reach an 
altitude of over 2000 feet that we come upon the boundary line 
between these lower beds and the higher zone of sericite schists. It 
would be quite unnecessary for us to here enter into any further 
details regarding the geological structure of these mountains. For 
those who would ask for further information on this point we would 
refer them to our papers in the Geological Magazine, where a more 
detailed account of their structure is given. 
At the end of the paper we have given a sketch map of a portion 
of Highland Perthshire, which will convey at a glance the relation¬ 
ships of the outcrop of this bed of schist to the high grounds upon 
which these plants occur, and also a section across Ben Lawers show¬ 
ing the position the same schist holds in that mountain. 
In conclusion, then, our contention is that in this band of sericite 
schist, whose positions we have just described, we have one of the 
most important factors in determining the distribution of our Alpine 
